Stretching from 3.2mm to 4mm

Hi yall!! So I’ve been 3.2mm for almost a year now and I bought a buffalo septum but the piercer said there was no size between 3.2 and 4 and that I had to stretch that size. I tried with coconut oil mutiples times, took a warm shower to dilate the septum but it doesn’t seem to go through, it hurts. I went from 2.5 to 3 then 3 to 3.2 with ease, and I really want to get to 4. Do you have any tips, products to use to get it in? Thanks💋